looking for best way of giving command line arguments in python, where some params are req for some option and some params are req for other options

Question

Hi i am trying to send command line arguments for first time. The condition is that one parameter is required for one option and for others other parameter.(looking for user friendly). The below code looks need some optimization:

import argparse
parser = argparse.ArgumentParser(description='Usage options.')
parser.add_argument('-o','--options',help='Options available: run,rerun,kill, resume,           suspend',required=True)
parser.add_argument('-c', '--config',help='config file input',type=file,required=False)
parser.add_argument('-j', '--id',help='id of the job',type=str,required=False)
args = parser.parse_args()
action_arg = list()
action_arg.append(args.options)
action = {'run': start_run,
          'rerun': start_rerun,
          'kill': kill_job,
          'resume': resume_job,
          'suspend': suspend_job,
          'get_run': get_run,
          'get_component': get_component,
          'help': print_help}.get('-'.join(action_arg))

if action:
    conf_file = str(args.config)
    jobid = str(args.jobid)
    if args.options == "run":
        if conf_file == "None":
            print "Job configuration is needed to start a run and job id is not needed"
            sys.exit(2)
    elif args.options == "rerun":
        if conf_file == "None" or jobid == "None":
            print "Job configuration and jobid is needed to start a rerun."
            sys.exit(2)
    else:
        if jobid == "None":
            print "Jobid is needed to perform %s action on job and configuration is not needed." %args.options
            sys.exit(2)
    action(conf_file, jobid)
else:
    print "Usage Error:"
    print_help()

Hope you get my required params for required options from code. Please let me know for detailed explanation on requirements

Answer 1

This variation on your script runs, and cleans up several things. It uses choices to control the options values. It omits unnecessary parameters in the other add_argument calls. It simplifies the post parse_args logic. help isn't really needed since there is always the -h option, but I included it as a choice. It falls through to the end because it is not in the action dictionary.

import argparse
import sys
class Stub(object):
    def __init__(self,s):
        self.s = s
    def __call__(self,conf_file, jobid):
        print self.s, conf_file, jobid
parser = argparse.ArgumentParser(description='Usage options.')
parser.add_argument('-o','--options', choices=('run','rerun','kill', 'resume', 'suspend','help'),required=True)
parser.add_argument('-c', '--config',help='config file input')
# optionals normally not required; 'file' not valid type
# argparse.FileType will open the file
parser.add_argument('-j', '--jobid',help='id of the job')
# str is the default type
args = parser.parse_args()
# action_arg = [args.options]
action = {'run': Stub('start_run'),
          'rerun': Stub('start_rerun'),
          'kill': Stub('kill_job'),
          'resume': Stub('resume_job'),
          'suspend': Stub('suspend_job'),
          #'get_run': get_run, # not in choices
          #'get_component': get_component,
          #'help': print_help,
          }.get(args.options)  # what's with the '-'.join?

if action:
    if args.options == "run":
        if args.config is None: # proper test for None
            print "Job configuration is needed to start a run and job id is not needed"
            sys.exit(2)
    elif args.options == "rerun":
        if args.config is None or args.jobid is None:
            print "Job configuration and jobid is needed to start a rerun."
            sys.exit(2)
    else:
        if args.jobid is None:
            print "Jobid is needed to perform %s action on job and configuration is not needed." %args.options
            sys.exit(2)
    action(args.config, args.jobid)
else:
    print "Usage Error:"
    parser.print_help()

This version replaces the options choices with subparsers. config and jobid become required arguments for the appropriate subparsers. I use parents to conveniently define the required mix and match. Now argparse does all the checking.

import argparse
class Stub(object):
    def __init__(self,s):
        self.s = s
    def __call__(self,conf_file, jobid):
        print self.s, conf_file, jobid

conf_parent = argparse.ArgumentParser(add_help=False)
conf_parent.add_argument('-c', '--config',help='config file input',required=True)
job_parent = argparse.ArgumentParser(add_help=False)
job_parent.add_argument('-j', '--jobid',help='id of the job',required=True)

parser = argparse.ArgumentParser(description='Usage options.')
parser.set_defaults(config=None, jobid=None) # put default value in namespace
sp = parser.add_subparsers(dest='options')
sp.add_parser('run',parents=[conf_parent])
sp.add_parser('rerun',parents=[conf_parent, job_parent])
sp.add_parser('kill',parents=[job_parent])
sp.add_parser('resume',parents=[job_parent])
sp.add_parser('suspend',parents=[job_parent])
args = parser.parse_args()

action = {'run': Stub('start_run'),
          'rerun': Stub('start_rerun'),
          'kill': Stub('kill_job'),
          'resume': Stub('resume_job'),
          'suspend': Stub('suspend_job'),
          }.get(args.options)
action(args.config, args.jobid)